1. Field of the Invention
This invention relates to methods, systems and apparatus for detecting, and preferably locating, changes in variables, especially liquid leaks.
2. Introduction to the Invention
A number of methods have been used (or proposed for use) to detect changes in variables along an elongate path, e.g. the occurrence of a leak (of water or another liquid or gas), insufficient or excessive pressure, too high or too low a temperature, the presence or absence of light or another form of electromagnetic radiation, or a change in the physical position of a movable member, e.g. a valve in a chemical process plant or a window in a building fitted with a burglar alarm system. Changes of this kind are referred to in this specification by the generic term "event". Such detection methods are for example highly desirable to detect leaks from steam lines into thermal insulation surrounding such lines, leaks from tanks and pipes containing corrosive or noxious chemicals, or leakage or condensation of water under floors or within telecommunication or electrical power systems. Some of these known methods not only signal when the event takes place, but also indicate the location of the event.
In recent years, substantially improved methods of detecting, and preferably both detecting and locating, events have been proposed and/or introduced into practice by the assignee of this application, Raychem Corporation. Reference may be made for example to copending, commonly assigned Ser. No. 372,179 filed June 27, 1989 which is a file wrapper continuation of Ser. No. 306,237 filed Feb. 2, 1989, now abandoned, which is a file wrapper continuation of Ser. No. 832,562, now abandoned, filed Feb. 20, 1986, by Masia, Reed, Wasley, Reeder, Brooks, Tolles, Frank, Bonomi, McCoy, Hauptly, Stewart, Lahlouh, Welsh, Nyberg and Klingman, and to the applications of which it is a continuation-in-part, namely
(1) Ser. No. 599,047 filed Apr. 11, 1984, by Masia and Reed (MP0869-US2), now abandoned, which is a continuation-in-part of Ser. No. 509,897, filed June 30, 1983, by Masia and Reed (MP0869-US1), now abandoned;
(2) Ser. No. 599,048, filed Apr. 11, 1984, by Masia and Reed (MP0869-US3), now abandoned, which is also a continuation-in-part of Ser. No. 509,897, filed June 30, 1983, by Masia and Reed (MP0869-US1), now abandoned;
(3) Ser. No. 556,740, filed Nov. 30, 1983, by Wasley (MP0892-US1), now abandoned;
(4) Ser. No. 556,829, filed Dec. 1, 1983, by Wasley (MP0892-US2), which is a continuation-in-part of Ser. No. 556,740, now abandoned;
(5) Ser. No. 618,106, filed June 7, 1984, by Hauptly (MP0920-US1), now abandoned;
(6) Ser. No. 618,109, filed June 7, 1984, by Reeder (MP0923-US1), now abandoned;
(7) Ser. No. 618,108, filed June 7, 1984, by Brooks and Tolles (MP0924-US2), now abandoned, which is a continuation-in-part of Ser. No. 603,485, filed Apr. 24, 1984, by Brooks and Tolles (MP0924-US1), now abandoned;
(8) Ser. No. 603,484, filed Apr. 24, 1984, by Frank and Bonomi (MP0932-US1), now abandoned;
(9) Ser. No. 691,291, filed Jan. 14, 1985, by McCoy and Hauptly (MP1020-US1), now abandoned;
(10) Ser. No. 809,321, filed Dec. 17, 1985, by McCoy and Hauptly (MP1020-US2, now abandoned, which is a continuation-in-part of Ser. No. 691,291;
(11) Ser. No. 744,170, filed June 12, 1985, by Stewart, Lahlouh and Wasley (MP1072-US1), now abandoned;
(12) Ser. No. 787,278, filed Oct. 15, 1985, by Stewart, Lahlouh, Wasley, Hauptly and Welsh (MP1072-US2), now abandoned, which is a continuation-in-part of Ser. No. 744,170, now abandoned; and.
(13) Ser. No. 831,758, filed Feb. 20, 1986, by Nyberg and Klingman (MP1094-US1), now abandoned.
Other commonly assigned applications to which reference may be made include
Ser. No. 856,925, filed Apr. 28, 1986, by Kamas (MP1121) now abandoned;
Ser. No. 017,375, filed Feb. 20, 1987, by Nyberg and Klingman (MP1094-US3);
Ser. No. 031,481, filed Mar. 27, 1987, by McCoy, Wasley, Wales and Edwards (MP1185); and
Ser. No. 057,459, filed June 3, 1987, now U.S. Pat. No. 4,843,321, by Koppitsch and Sparling (MP1197).
Earlier methods for detecting events are disclosed for example in U.S. Pat. Nos. 1,084,910, 2,581,213, 3,248,646, 3,384,493, 3,800,216, 3,991,413, 4,278,931 and 4,400,663, U.K. Pat. Nos. 1,481,850 and 182,339, and German Offenlegungschriften Nos. 3,001,150.0 and 3,225,742. The disclosure of each of these patents is incorporated herein by reference.